Adderall is not produced in the UK thus it is not a licensed drug. However, due to it’s amphetamine salts based, this drug is scheduled in the UK as a Class B controlled substance (like weed, hydrocodone and any other controlled medicines). Therefore Adderall is considered as not legal drug for import, and it is not legal to buy adderall in the UK unless you have a special prescription from the UK doctor. The process of Adderall acquiring it will be similar to how you would acquire other illegal drugs.
To be treated with Adderall in the UK, you would need to find a psychiatrist (not just a regular pharmacist or doctor of any other (than psychiatrist) practice who might be able to write an “Off Label” script. If you purchase Adderall from the US, you will have to make this script (issued by the UK doctor) to be delivered along with your adderall order. Sadly, the procedure of getting Adderall to the United Kingdom will be lumbering, tedious, and definitely would be a costly event.
Another solution is modafinil, the best alternative to adderall available in various online stores. This substance is less addictive with lack of side effects. One can purchace 3 months supply of this drug for perosnal use. The legality of possession of modafinil is still unclear.